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Validation is one of the most important parts in any software project. Building flexible business validation is every one’s dream. Rather than writing frameworks from scratch to do these things, Microsoft validation blocks makes it a breeze. In this article we will discuss how validation application blocks help us to build flexible validations using validation application blocks. Its just a simple sixteen step process to put our business validation in action using validation blocks.

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No business can work without validation. Software’s are made to make business automated so validation forms the core aspect for any software. Almost 80% projects in .NET implement validation as shown in figure below.

Figure: - Validation implemented

The above figure shows how business validations are implemented for a simple customer class. We have two properties customer code and customer name. Both of these properties are compulsory. So we have created a class called as ‘ClsCustomer’, with two set/get properties for customer code and customer name. If we find that customer code is empty in the set of the property we raise an error. The same methodology we have used for customer name.

Now we can consume the class in the ASPX UI as shown in figure ‘Business object consumed’. We have created the object, set the properties and in case there is error we have caught the same and displayed it in a label using try catch exception blocks.

Figure :- Business object consumed

This implementation looks good to some extent as we have put the business validation in the class and decoupled the UI from any business validation changes.

Let’s list down the common problems associated with the above methodology:-

Tangled validation: - If the validation rules changes we need to compile the whole class. As the entity and the validation layer are entangled in one class, changes in validation leads to compilation of the whole class. So out first goal should be decouple this validation logic from the entity class. When we say entity class we are referring to the ‘ClsCustomer’ class.

Figure :- Tangled validation

Figure :- Decoupling validations from the entity class

No need of compiling: - Validations are volatile entity. They change from time to time. If we can change validation constraints without compiling will lead to better maintenance of the system.

One go validation and results: - The second issue is validations are executed in every set of the property and errors are displayed one by one. It would be great if we can validate all the validation once and display all the errors once.

All these things can be achieved by using Microsoft validation application blocks.

Step 2:- Once you install it you should see the same in programs – Microsoft patterns and practices.

Before we move ahead to understand how validation application blocks works. We will first walkthrough fundamentally how validation application blocks decouples the validation from the entity classes. Validation application blocks stands in between the entity class the validation. Validations are stored in configuration files like web.config or app.config depending whether it’s a web application or a windows application. So the validation blocks reads from the configuration file the rules and applies it over the entity class. We can maintain these validations using the enterprise configuration screen provided by Microsoft blocks.

Figure: - Decoupling validations from entity classes

Now that we have understood how validation blocks will work. We will run through a example practically to understand the concept.

Step 3:- Once you have installed the block, click on Enterprise library configuration UI to define validation on the configuration file

Figure :- Loading Enterprise configuration screen

Step 4:- Click on open and browse to your web.config file and click the open button.

Figure :- Open the web.config file

Step 5:- Once you have opened the web.config file you should see a tree like structure as shown in figure ‘Add validation block’. Right click on the main tree and add the validation application block to your web.config file.

Figure :- Add validation application block

Step 6:- Once you have added the validation application block you should see a validation application block node. Right click on the node , select new and click the type menu.

Figure: - Add the assembly type

Step 7:- Once you have clicked on the type menu you should see a dialog box as shown in figure ‘Load assembly’.

Figure: - Load assembly

Step 8:- Click on load assembly and browse to the assembly DLL to which you want to apply validations.

Figure: - Browse the assembly

Step 9 :- Select the class in the assembly as shown in figure select class.

Figure :- Select class

Step 10:- Once you have loaded the assembly, you should see a new node ‘MyRules’ as shown in figure ‘Choose members’. Right click on ‘MyRules’ ? new and choose members.

Figure: - Choose members

Step 11:- Once you have clicked the choose members menu you will be popped up with a property selector box as shown in figure ‘Select properties’. In the customer class we have two properties on which we want to apply validations one is the customer name and the other is the customer code. So we will select both the properties and click ok.

Figure: - Choose properties

Step 12:- Once you have selected the properties you can see both the properties in the UI. To apply validation right click on let’s say customer code property. You will now see list of validations which you can apply on the property. This tutorial will not go in details about all the validations. If you are interested in the same you can read about it more on http://msdn.microsoft.com/en-us/library/cc309336.aspx . For the current scenario we will select range validator.

Figure: - Select range validator

Step 13:- Once you have selected range validators, you will see the below property box for range validators. In this particular scenario we need that both the property i.e. customer code and customer name should not be empty. So in the lower bound we will put 1 , which signifies that at least one character is needed. In the lower bound type we have selected as inclusive, which means the lower bound check is compulsory. In the message template put the error message which you want to display in case there are issues.

Figure: - Range validator properties

Step 14 :- In the default rule select the rule which you have just made. If it’s none validations will not fire.

Figure: - Select rule

If you are done just save everything and watch your web.config which is now modified with the validation tags. You will see both the validation i.e. customer name and customer code in XML format inside the <validation> tag. The best part of the config file is now you can change the validation in the config file itself.You guessed right… no recompiling , no installation and completely decoupled.

Figure: - Web.config with validation tags

Step 15:- Ok, now that we are done with putting the validation in the web.config file. Its time to write the code which will read from the config file and apply to our entity class. So the first thing we need to reference the validation application block in our assembly references and include the name spaces in our clsCustomer class.

Figure: - Reference validation application blocks

Figure: - Import the validation namespace

Step 16:- Once you are done with adding the namespaces its time to fire the validation. Below is the code snippet which shows how the validation application block fires the validation using the web.config file. First step create the customer object and set the property. In the second step we tell to the validation static class to validate the object. The validation static class returns validation results. This validation results are nothing but error failures in case the validation fails. In the final step we have looped through the validation results to display the error.

Figure: - The validation code

Ok, now that we are done its time to see the action. You can see in the UI we have just set empty properties and it showed me both the business validations errors from the collection.

Figure :- Validation in action

The other problem with validation is that it only does server side you can read my tutorial how we can generate client side validators using validation engine at ApplicationBlock.aspx

Comments and Discussions

Unable toload the assembly. The error message is'could not load file or asembly
file///c:Users\Admin\AppData\Local\Temp\tmp99CE.tmp'or one of its dependencies. This assemblyis built by a runtime newer than the currently loaded runtime and can nto be loaded

i get an error when i run webpage is it solve by enterprise library configration
Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.

I am not using Microsoft Validation Block but I have question regarding separating validation classes. Having one validation class per entity or keeping all validation one class. If you have same field in all entity class then which design will be better?

I like your article. I have one question. How to write rules into text file instead of .config file.
I have lot of fields(i.e. 50). I have to validate all fields. If we use .config file, .config is having lot of codes. I want to maintain into text file. Is there any way to do it?

Hi !
Thank you very much for your article. I'm using Enterprise Library and I didn't know how making validation until now ! ^^
But, my application is localizable... So, how can I put the Message Template in a Ressources file ?

I will definetly make it a point to put source code.In all recent articles i have started putting in source code. Agreed until we do not show something substantial we can never know if it works.Agreed and noted.

What if I go "customer.CustomerName = null;"? Your code will end up throwing "Object reference not set to an instance of an object" on the "if (value.Length == 0)" line, rather than "Customer name is compulsory".

Best to do it like this:

if (string.IsNullOrEmpty(value))
{
thrownew Exception("Customer name is compulsory");
}

I agree. What is presented in this article seems like overkill - it's too much for small applications. I'd go with the typical mutator validation behavior, and for anything more complex I'd throw in PostSharp.

Hi Shivprasad, I'm working with Validation Application Block (Enterprise Application Block 3.1). I need to keep the rules on multiple configuration files. For example, in your demonstration, you work with the class Customer, I work with three classes: Customer, Order and Invoice. I need that for every class there is a configuration file with their respective rules, but I do not know how to make all this work together. I am grateful for your attention.

I beleive you can access multiple config file or section. I think there is a method Validate.ValidateFromConfig or Validate.OpenFromConfig instead of Validate.Validate() that will use the default app or web.config or create by a different ruleset!!! You can have multiple rulesets per class!

Good article.
Two things that in my opinion would improve your article.

1. Always have a brief but detailed article 'description' as it is shown in the list of articles. Never just repeat the title like you have done as it does not encourage me to read your article because it does not tell me anything about it.

2. Always have some code associated with the article as a demo. I don't think it matters with this article but there are a number of peasants out there that don't actually read the articles, they just want to rip off the code.